Multi-functional anodes boost the transient power and durability of proton exchange membrane fuel cells.

Proton exchange membrane fuel cells have been regarded as the most promising candidate for fuel cell vehicles and tools. Their broader adaption, however, has been impeded by cost and lifetime. By integrating a thin layer of tungsten oxide within the anode, which serves as a rapid-response hydrogen reservoir, oxygen scavenger, sensor for power demand, and regulator for hydrogen-disassociation reaction, we herein report proton exchange membrane fuel cells with significantly enhanced power performance for transient operation and low humidified conditions, as well as improved durability against adverse operating conditions. Meanwhile, the enhanced power performance minimizes the use of auxiliary energy-storage systems and reduces costs. Scale fabrication of such devices can be readily achieved based on the current fabrication techniques with negligible extra expense. This work provides proton exchange membrane fuel cells with enhanced power performance, improved durability, prolonged lifetime, and reduced cost for automotive and other applications

Power-line communications: smart grid, transmission, and propagation

1 School of Informatics, College of Informatics and Virtual Education, University of Dodoma, P.O. Box 490, Dodoma, Tanzania 2 Electrical Engineering Department, Faculdade de Engenharia, Federal University of Juiz de Fora, Campus Universitario, 36 033 330 Juiz de Fora, MG, Brazil 3Wireless and Power Line Communications Lab, Universita di Udine, 33100 Udine, Italy 4 France Telecom, Orange Labs, 2, Avenue Pierre Marzin, 22 307 Lannion Cedex, Franc

Failure Mode, Effects and Criticality Analysis of a Very Low Earth Orbit CubeSat Mission

When space programs launch vehicles into orbit, multiple failures could arise throughout the mission and corrective actions are often not an option. Applying reliability engineering approaches during the design phase focuses on analyzing risk by anticipating potential failures and mitigating uncertainties in the design. Old Dominion University, in partnership with the U.S. Coast Guard Academy, and the U.S. Air Force Institute of Technology designed and developed a 3U CubeSat mission to validate on-orbit, three space technology payloads. Mission SeaLion will fly as a secondary payload on stage two of Northrop Grumman’s Antares rocket and will be deployed in a very low Earth orbit the spring of 2023. Mission SeaLion will have multiple custom-built components on-board that have no space flight history that includes the Interface Board, Electrical Power System, and deployable composite structure payload. Custom-built components are a much higher risk to mission SeaLion when compared to space proven commercial off-the-shelf components. Engineering students at universities rarely have hands-on engineering experience in the field. Experts at NASA Langley Research Center provided guidance with identifying potential failure modes for the custom-built components. The potential risks of failures were evaluated using the Failure Mode, Effects and Criticality Analysis in efforts to increase the reliability of mission SeaLion. Mitigation strategies for each potential failure mode will include either a redesign or functionality, vibration, and vacuum chamber testing. Applying redesigns to the printable circuit board, battery pack, electrical connectors, and implementing rigorous inspection criteria significantly increased the reliability of the electrical systems. Execution of test plans using a thermal vacuum chamber will simulate space condition, which will verify deployment of the payload and ensure that electrical components function as designed

Vector sensors for underwater : acoustic communications

Acoustic vector sensors measure acoustic pressure and directional components separately. A claimed advantage of vector sensors over pressure-only arrays is the directional information in a collocated device, making it an attractive option for size-restricted applications. The employment of vector sensors as a receiver for underwater communications is relatively new, where the inherent directionality, usually related to particle velocity, is used for signal-to-noise gain and intersymbol interference mitigation. The fundamental question is how to use vector sensor directional components to bene t communications, which this work seeks to answer and to which it contributes by performing: analysis of acoustic pressure and particle velocity components; comparison of vector sensor receiver structures exploring beamforming and diversity; quanti cation of adapted receiver structures in distinct acoustic scenarios and using di erent types of vector sensors. Analytic expressions are shown for pressure and particle velocity channels, revealing extreme cases of correlation between vector sensors' components. Based on the correlation hypothesis, receiver structures are tested with simulated and experimental data. In a rst approach, called vector sensor passive time-reversal, we take advantage of the channel diversity provided by the inherent directivity of vector sensors' components. In a second approach named vector sensor beam steering, pressure and particle velocity components are combined, resulting in a steered beam for a speci c direction. At last, a joint beam steering and passive time-reversal is proposed, adapted for vector sensors. Tested with two distinct experimental datasets, where vector sensors are either positioned on the bottom or tied to a vessel, a broad performance comparison shows the potential of each receiver structure. Analysis of results suggests that the beam steering structure is preferable for shorter source-receiver ranges, whereas the passive time-reversal is preferable for longer ranges. Results show that the joint beam steering and passive time-reversal is the best option to reduce communication error with robustness along the range.Sensores vetoriais acústicos (em inglês, acoustic vector sensors) são dispositivos que medem, alem da pressão acústica, a velocidade de partícula. Esta ultima, é uma medida que se refere a um eixo, portando, esta associada a uma direção. Ao combinar pressão acústica com componentes de velocidade de partícula pode-se estimar a direção de uma fonte sonora utilizando apenas um sensor vetorial. Na realidade, \um" sensor vetorial é composto de um sensor de pressão (hidrofone) e um ou mais sensores que medem componentes da velocidade de partícula. Como podemos notar, o aspecto inovador está na medição da velocidade de partícula, dado que os hidrofones já são conhecidos.(...)This PhD thesis was supported by the Brazilian Navy Postgraduate Study Abroad Program Port. 227/MB-14/08/2019

Study of mm-wave Fixed Beam and Frequency Beam-Scanning Antenna Arrays

Millimeter-wave frequencies are anticipated to be widely adapted for future wireless communication systems to resolve the demand of high data-rate and capacity issues. The millimeter-wave frequency range offers wide spectrum and a shift for most newly developing technologies as the microwave and lower frequency bands are becoming overcrowded and congested. These high frequency bands offer short wavelengths which has enabled the researchers to design and implement compact and adaptable antenna solutions. This research focuses on the implementation, transformation and modification of antenna structures used in lower frequency bands to millimeter-wave applications with high gain and multi-band and wideband performances. The first part of the thesis presents a microstrip patch array antenna with high gain in the upper 26 GHz range for 5G applications. The tolerance of the antenna, on widely used Rogers RT/duroid 5880 substrate, is observed with the edge-fed structure when curved in both concave and convex directions. In the second part of the thesis, 20 rectangular loops are arranged in a quasi-rhombic shaped planar microstrip grid array antenna configuration with dual-band millimeter-wave performance. A comparison with equal sized microstrip patch array is also presented to analyse the performance. The antenna operates in the upper 26 GHz band and has two frequency bands in close proximity. The third part of the thesis discusses the transition from wire Bruce array antenna to planar technology. Having been around for nearly a century and despite the simplicity of structure, the research community has not extended the concept of Bruce array antenna for further research. The proposed planar Bruce array antenna operates in three frequency v bands with optimization focus on 28.0 GHz band that has a directive fan-beam radiation pattern at broadside whereas the other two frequency ranges, above 30 GHz, have dual-beam radiation patterns which provide radiation diversity in narrow passages. The final part of the thesis deals with the transformation and modification of wire Bruce array antenna geometry to edge-fed printed leaky-wave antennas for millimeter-wave frequency scanning applications. In the first approach, the lengths of the unit-cell are optimised, without any additional circuitry, to enable two scanning ranges and mitigate the Open-Stopband, at broadside, for seamless scanning in the first range. A Klopfen-stein tapered divider is then deployed to make a linear array of the proposed antenna to achieve high gain. In the second approach, the horizontal and vertical lengths of the meandered unit-cell are replaced with semi-circular and novel bowtie elements, respectively, to obtain wide scanning range. The numerical results and optimizations have been performed using CST Micro-wave Studio where the effects of metallization and dielectric losses are properly consid-ered. The prototypes of the proposed antennas have been fabricated and experimentally validated

Modified Timed Efficient Stream Loss-tolerant Authentication to Secure Power Line Communication

This paper investigates the feasibility of Timed Efficient Stream Loss-tolerant Authentica- tion to serve security needs of Power Line Communication (PLC) system. PLC network has been identified as the ideal choice to function as the last mile network, deliver load management messages to smart meters. However, there is need to address the security concerns for load management messages delivered over power line communications. The ubiquitous nature of the power line communication infrastructure exposes load management systems (LMS) deployed over it to a security risk. Ordinarily, PLC network does not em- ploy any security measures on which the smart meters and data concentrators can depend on. Therefore, the need to provide a secure mechanism for communication of load man- agement system messages over a PLC network. In LMS, source authentication is of highest priority because we need to respond only to messages from an authenticated source. This is achieved by investigating suitable robust authentication protocols. In this paper we present modifications to Timed Efficient Stream Loss-tolerant Authentication for secure authentica- tion to secure messages for load management over PLC. We demonstrate that PLC can be used to securely and effectively deliver Load Management messages to smart meters, with minimal overhead.